Pulse modulation sound recording system



2 Sheets-Sheet i June 6, 1950 G. J. LEHMANN ETAL PULSE MODULATION SOUNDRECORDING SYSTEM Filed April 17, 1945 June 6, 1950 G. ,1. LEHMANN ETAL2,510,121

PULSE MODULATIDN SOUND RECORDING SYSTEM med April 17, 1945 2sheets-sheet 2 ATTORAEY Patented .une 6,

PULSE MODULATION SOUND RECORDING SYSTEM Gerard J'. Lehmann, New York,and Norman H. Young, Jr., Jackson Heights, N. Y.,assignors to FederalTelephone and Radio Corporation, New York, N. Y., a corporation ofDelaware Application April 17, 1945, Serial No.`'588,846 i Claims.

This invention relates to methods and means for recording intelligenceand more particularly to recording intelligence in the form of discretestrips or line segments.

Many methods of using the full area of photograhic lm ribbons forrecording intelligence have been proposed in the past. One of theoutstanding methods from the viewpoint of sound recording is theproposal to scan the lm in lines from side to side as the iilin is beingsteadily advanced lengthwise.v This permits oi a much greatervlinearspeed of progression of the scanning spot along the track, thus ailowingthe recording of higher frequencies.

One fundamental drawback of this system, however, is the diiiiculty ofremoving components synchronous with the scanning rate caused b3,transients at the instant the end of one line is reached and thescanning of the following line is begun.

It is Van object of our invention to provide a method and means whicheliminates these undesirable transients as the scanner of a, striprecorder leaves one discrete line and begins to scan the following line.

-It is a further object of our invention to provide method and means torecord intelligence having the character of a continuous function in theform of an intermittent wave or pulse form.

It is still another object of our invention to provide method and meansto record intelligence in discontinuous strips or lines by means ofpulses the rate of which is synchronized with the scanning in such amanner that no recording takes place at the junction point of two lines.

In accordance with one feature of our invention we lirst convert acontinuous type of intelligence such as sound into discrete pulses whichare modulated in respect to one of their characteristics in accordancewith the intelligence. These modulated pulses are used as a control forthe intensity of a light beam which is made to act on a photographicnlm. The light beam is made to scan substantially the full width of thefilm, as the film is being moved lengthwise, and'to begin scanning thenext line, as the scanning of one given line is completed, by means of arotating scanning mechanism. The rotation of the scanning mechanism issynchronized with the generation of the pulses which are modulated by`the intelligencesuch that no pulses occur at the junction points of anytwo scanning lines. Therreproducer of the recorded intelligence mayutilize the same type of scanner and film mechanisrn except that in thisc ase the light beam may be made to -va'rythe output of a photo-electriccell in accordance with the film record.

Theseandother features and objects of our invention will become moreapparent upon consideration of the following detailed description to beread in connection with vthe accompanying drawings in which:

Fig. l is a schematic representation of a system for recordingintelligence on a film inaccordance Ywith thel invention;

l'ig. 2 showsthe-relation of certain parts o f the system of Fig. 1inapartial section thereof along the line 2--2;

Fig. 3 is a series of graphs illustrating in -part the operation of thesystem of Fig. 1;

Fig. 4 is an alternative recording system embodying our invention; 'f fFig. 5 is as'chematic representation of a, system for reproducing theVintelligence recorded on aphotographic ilm -in accordance with thesystem of Figs. 1 and 4;

Fig. 6 is a plan view of va portion of a nlm bearing recordedintelligence; and 1 Fig. 7 shows the character of the recordedintelligence and its relationship to the scanning cycle. Y l

' Referring now to the Fig. 1, the recording system comprises a pulsegenerator I which may be of the type disclosed in Figs.'3 and 6 of theapplication for patent -byv E. Labin et al., Ser. No. 455,897, filed,August'24, V1942, now U. S. Patent No. 2,416,329, granted Feb. 25, 1947.Since this type of pulse-generatorlhas been disclosed before. nodetailed description thereof will be given in this case beyond thestatement that it is a so-called cusper wave generator, that is, onewhich converts a, vsine wave into a series of cusps by therecticationwof one-half of the wave with respect to a non-symmetricalbase or zero axis. The cusps of the resulting wave are varied in respectto their Widthfand/Or their phase in accordance with intelligence from amicrophone 2 and then clippediand shaped in the form ofj discrete pulsesYat 3. Y

The modulated'pulses (are used to vary the intensities of a' light; beami4 emanating from .a lamp or lightsource 5.. .Thelight beam 4 is made tostrike a mirror assembly 6 mounted in the axial center of alense-drum 1. This drum is provided with 4 setsiof lenses 8 spacedaround its .peripheral wall at intervals.'V The light beam.is deflectedby means of the. mirror. assembly 6 and concentrated by means of thefour lenses 8 to scan in a concentrated form 9.a lm IIJ being movedgin adirectionV l l by/ means of a sprocket I 2,

3 This sprocket wheel I2 may be driven by a motor I3 over a mechanicalconnection indicated at I4. Motor I3 may also serve as the drive for thelense-drum 'I through the medium of a shaft I5. The motor I3 carries onits free end I6, a

lrotor Il for a phonic generator which includes.

the toothed rotor Il and a magnet and coilaggre. gate I8 placed inproximity to the rotor I'I. In the coils of the magnet I8 in cooperationwith the magnetized teeth of the rotor I1 there is generated asinusoidal voltage which by Wayof. conductors I8, is applied to asmoothing filter circuit 28.

After the elimination of theundesirable har;- monics at 20, the wave isappliedtoenergize-fthe. pulse producer and modulator. I.. As seen inthe. sectional View of the lense-drum and the film,

I the iilm is held in curved form across its Width so as to avoiddistortion of the record due.- to the circular movement of thescanningbeam 8. The scanning width isdened bymeans o f masks 2l and 22 disposedalong the edgesnof the film. The

The graph a,V of Fig. 3. indicates the type of,

sinusoidal voltage Which-may b euobtained from the phonic generatorI`I-I8.,

In graph b there are shownthecnsper wave as obtained from thessine Waveat-a fromthe pulse or cusper modulator I andithere mayibe seenfat c,

pulses as obtained from 'the Shaper; 3,- after-the cusps are clipped andaniplirfied;U TheV s igniicance of these graphs will be further;discussed` in' connection YWiththe0.11eration, o f.. the. systemhereinbelow.

An alternative system for recording intent,-v

gence as shown in Fig, 4 includesan oscillator 24; which on the onehandenergizes a sweep circuit 25u to produce a conventional saw-tooth,sweep for the lateral-displacementaof all electron, beam in a cathoderay. tube, 2,6,4 through themedium of deflectioncoilsrZ'I, graphd ofFig. 3v illustrating the type of safvrtooth sweepwliiclil may be used inthis case o n the other hand, ,the

oscillatorA 2li also serves toenergize apulsemodulater 28 Whichmay be.of theVv formdescribed in` connectionwith the system of Fig .1, that is,it. The pulses .Obtainedy may be of the cusper type. from the cusps aremodulated intimegby intelli gence signals from microphoneZSl, thenshaped at v3,() and then used tomodulate theintensity ofl the beam ofthe cathode raytube 26; This vbeam` is applied through the medium of; alense 33 to a photographic film 3l which-isprogressvely moved asindicated by thearrow 32.

In Fig. a system for reproducingthe intelligence from the iilmasrecordedby the system of` Figs. 1 and 4 isshown tocomprise a source oflight 34 which emits a lightv beam 35. This light beam 35, similarly tothe arrangement usedV in Fig. 1, is made to fall on a lm, which is beingmoved longitudinally, throughthe medium-ofv a deflecting mirror assembly31 and a lense system 381spaced as above at 90'intervals around thecentral-wallportion of alense-drum 391whichisv rotated about itslongitudinal axis. In accordance with the recorded intelligence thereon,the film 36 permits a light beam 40 with correspondingly varyingintensity to act on a light-sensitive cathode 4I of a photo-electriccell 42. Voltages proportional to, these varying. intensities obtainedfrom= an anode 4,3 areA then in aA conventional manner applied to anamplier 44, a demodulator 45, a low pass lter 45, and are finallyutilized in an audio device such as earphones 41.

In- Fig; 6; a portion of a lm bearing recorded intelligence is showncomprised of a transparent photographic nlm 48; which has been providedwith apertures'llffor cooperation with a sprocket and isshownto have avarying transparency in the form of recurrent dark pulses 58 which arespaced fromone another in accordance with the original modulatingintelligence.V The pulses 50 are. formed'l into discrete and separatelines or strips across the width ofr the film as at 5i, 52, 53.

In Fig. '7v the'lines 5I 52.; 53, areVv showntin sequentialrelationship. and;A referred to, ax comfmonhorizontal baseline for a.betterfunderstandr ing of the invention.

In recording intelligence in accordance. with the system ofV Fig. 1,theA pulsesv which may.. be;

obtained as already indicated from the cusper; type pulse generator Ibygsubjecting thev sinus,. oidal Wave ofI Fig, 3d tov an effectivefullzwaveg rectification. As disclosed the.l abovernamed application,Ser. No, 455,897' the rectification`r preierablyfmay takeplace-,bymeans-,offa biased;

full wave rectifier, that,is, about an:v oiset zerd axisindicated,bythebrokenfline 5,4.v 'heeuspel wave at Y in Fig.Blz-indicates the unmodulated ormvof` a sine Wave,l as rectiediaboutfitsoffset' axis 54.. The signaldntelligenceapplied throughV the modulator,2fserves-in effect todvaryfthersine.. wave of Fig. 3 0, relativeto,itspoffsetgaxis.54-With1 regard to its full wave rectification.Tl,iis.,=11e1:J.-.A tive variation between 4the-wave andthe ZerQiaxisthereof is illustrated-inFig.,Sa-byfthQupper/and; lowery modulationlimits, 5.6.-; and; ,51; When@V the:y

applied signali varies;l the;., relatiye, relation be tween the offsetaxis 54 andthe.sinewave. toan-lv` extent as indicatedby the; lower-limit5.1;the cusper-wave 5,5,y for example,.isdisplac ed tcha-` position as.shownf` by the4 broken` line- 5.8,` and;

when it` isvaried to the,l displacement,limit-53..

the cusper waveis; displaced; asshown by.l the broken linevr59. VItwillbeobserved thatthefsig.A nal WavethusY varies-:the time;pesitionsiofeusps'.

60, 6|. 62, 63,;flrinrpushfpulhtoward andaway-f fromeachother, therebydecreasing orf-increase.

ing the time 5 interval 4 between;V successive;v cusps;M

For reordingpurposes .the cuspsf are, preferably clipped fr0m.the.waveandishanedzif desired, tot

form rectarigular;V pulses.; itloeingunderstood Ltiat'A'v other.7 knownshapes maybeused instead,l The:

cusps may. be .clipped-1betweentheflmits;Giganti.-

66 by means of a; gatezclipperf Whichimay formi.v

a part of the shaper 3,;Fig.\.1. VInaccordancewitm the circuitparameters of lthe gate clipper which.

- determines .the cusper wave portion'.between..-

these limits, apulse--shape suchlas rshown-.ati 621i inFig. 3cmay,be-produced. Due-to the-variation oft the base aboutwhich-thesinewave of liigrSa'v may be rectied between vthe limitsand 51 the resultingpulses willlvary in phase-betweenthek as just described the pulses maybe modulated in amplitude or in width, or the pulses may consist ofshort-bursts of a frequency modulated oscillatory energy. The pulsesthus modulated are one of several possible methods serving to Vary theintensity or the width or other characteristic of the light beam 4 9impinging on' the nlm I0. From the sectional view in Fig. 2 it isevident that due to the rotation of the lensedrum 1 the recording lightbeam 9 travels across the width of the film starting at the point 1I)defined by the inside edge of the mask 22 to a point 1I which isdetermined by the inside edge of the mask 2i. These scanning limits arealso indicated by the lines and 1I on the lm portion in Fig. 6. As thelight beam crosses with Width of the film' along the scanning lines 12(Fig. 6), the nlm advances in the direction of the arrow 13. Thus, forinstance, if a light beam has traveled across the width of the iilm andreached the line 12, a beam following it by 90 has come into place forscanning, so that, at the instant the first beam is blocked by the mask2 I, another beam is appearing from behind the mask 22 to continue thescanning where the preceding beam has left off, that is, as soon as thelm has advanced for the next scanning line 1I to be in position. Thus,by the proper adjustment of the masks 2I and 22 the interval t (Fig. 7)between the end of the line 5| and the beginning of the next line 52(Fig. 7) may effectively be made zero. Since the rate of occurrence ofthe pulses which carry the intelligence is governed by the sine wave ofFig. 3a, as generated by the phonic generator I1-|8, and this generatoris driven by the motor I3, which also determines the speed of thescanning beam 9, the scanning operation with respect to the progress ofthe film' and the occurrence of the pulses may be synchronized such thatno pulses will occur past the end or the beginning of any scanninginterval ts (Fig. 7). This is brought about by a suitable adjustment ofthe horseshoe magnet I8 with respect to the teeth 23 so that the peaksof the sine wave produced by the generator I1-I8, corresponding to thetroughs of the cusper wave 55 occur substantially coincidental with thebeginning or the end of the scanning intervals. This arrangementeiectively prevents the recording and transmission or reproduction ofany intelligence at the point of junction between scanning lines 12. Forthe purposes of illustration the scanning time interval ts has beenshown to comprise two com- Dlete cycles of the sine wave in Fig. 3a.

In recording intelligence by means of the system of Fig. 4, similarconsiderations are applicable, except that the adjustable cathode raysweep circuit here takes the place of the adjustable light beam masks ofFig. 2. The oscillator 24 generates the sine wave in correspondence tothe phonic generator of Fig. 1, which energizes the pulse generator andmodulator 28-29. The intensity of the electron beam sweeping across withwidth of the lm 3| is modulated in accordance with the intelligence. Theextent of scanning or of the sweep of the beam is regulated by suitableadjustments of the circuit and the deflecting coils 21. Here, too, theextent of the sweep or scanning interval ts is maintained in the desiredrelationship to the pulse generating sine wave by means of theoscillator 24 which is common to the sweep and pulse circuits 24. Aslight difference exists between the cathode ray recorder and the systemof Fig. 1 in that the time interval t in the case of the former systembeiIl tween the end of one scanning line and the beginning of the nextis theoretically never zero as is the case in the latter system, sincethe return of the recording cathode ray takes a certain, if small,amount of time tr (Fig. 3d). As indicated at Fig. 3d, the saw-tooth typevoltage governing the lateral sweep of the cathode ray is timed such asto return to its starting point to coincide with the selected peak ofthe sine wave, the occurrence of the interval tr being chosen so that nopulses will occur at that time.

It is thus evident from the above that the occurrence of transients atthe instant the end of one line is reached and the scanning spotV isbeginning to scan the following line has been effectively eliminated.

From the foregoing description it is clear that our invention provides asuperior system for audio frequencies up to 15 thousand cycles whichpossesses a denite improvement in its signalto-noise ratio as comparedto other sound tracks now in use, and running longer per foot of film.

It should also be noted that another application of this method is thepreparation of high delity transcriptions for radio stations and othersusing sound only.

Another advantage of recording continuous Wave intelligence by means ofdiscrete pulses as proposed above, even if a synchronization of thepulse occurrence rate and of the scanning beam is not feasible, is thatany transients occurring at the junction points of the strips or linesmay also be removed by blocking circuits, any signicant intelligencethus not being lost at that time.

While We have described above the principles of our invention inconnection with specific apparatus, and particular embodiments thereof,it is to be clearly understood that this description is made by Way ofexample only and not as a limitation on the scope of our invention asset forth in the objects and the accompanying claims.

We claim:

1. A system for recording intelligence comprising a pulse generator, amodulator for modulating pulses in accordance with said intelligenceleaving a given minimum time interval between successive pulses, arecording lm having means for moving it lengthwise, means for recordingthe intelligence in its modulated pulse form on the lm in separatestrips, each strip running across the width of the film within givenlimits, and means for synchronizing the timing of the recording of eachstrip with respect to the timing of the pulses so that said minimuminterval between given pulses substantially corresponds with the periodbetween the end of recording of one strip and the beginning of therecording of the next strip.

2. A system according to claim 1, wherein said lm is a photographicallyrecording film and said means for recording includes means for producinga beam of light, means for modulating said beam in accordance with saidmodulated pulses, means for repeatedly moving said beam across said lmlaterally thereof within said given limits, the lengthwise movement ofthe lm being so related to the beam movements that successive movementsof the beam across the film are separated, said synchronizing meansincluding means timing the beam movement with respect to the pulseoccurrence so that the pulse intervals substantially correspond to thehiatus between one recording movement of the beam and the next.

2li 510g a; asystemnfar fcrd-ing mtemgnceon sound comprisingmeans..forproducing recurrent dis-1A 'creteL pulses in accordance' with? the.intelligence or sound', means. for modulating the. beam of a cathoderaytube in accordance withv said modu; lated: pulses and a sweep circuitfor repeatedly scanning al photographic recording 'flm at'spacedintervals across its. width. by the said cathode ray tublewithin givenlimits of 'said width and: means.I forsynchronizing theA occurrence ofsaid pulses with that of said scanning, Aso that intervals bee. tweengiven pulses substantially correspondf to the. hiatus. betweensuccessive scannings.

4; A system for recording intelligence or sound. comprising means forproducing recurrent dis! crete pulses modulated in accordance with theintelligence; means for modulating a beam of lig-htiin accordance withsaid modulated' pulses, arecording lm`A having means. for moving itlengthwise, means for repeatedly scanning said across its'` width by"said lig-ht beam at a given'r'ate at .spaced intervals and within givenlimits of said width, said means for scanning including an opticalsystem for directing saidlLig-ht beam towardv said lm, means forrotating said system and means for `ad--justably masking said directedbeam initiallyand finally with respectto said scanned width and meansfor synchronizing 'the occurrence ofr said pulses with that 'of saidscanning so` that inter-vals between given pulses substantiallycorrespond to the hiatus between successive scannings.

A system for recording intelligence or sound comprising means forproducing recurrent discrete pulses modulated in accordance with theintelligence, means for' modulating a beam of light in" accordance withsaid modulated pulsesI4 8 a recording. nlm having means for'moving itlengthwise, means for-` repeatedly scanning. said lmacrossits width bysaidlight beam at a given rate. at fspaced intervalsy and. within.given. limits of: said-fwidthgfand'means for synchronizing theoccurrence of said' pulses with that of said: scanf' ning sothatintervals between given pulses sub.-A staiiizial-lyv correspondtothe hiatus between suc. cessive scanningsyincludng means for rotatingsaid-meansior?scanning. at a. given rate, means for. generatingy asinusoidal voltage synchronous with said 4given rate,` and. means lforapplyingJ said Voltage; for-energizing said. means for modulating saidpulses, wherebythe occurrence. oft'said pulses isis-yn'chronized withthe` rate. and extent of vsaid scanning. GERARD. J. LEHMANN.

NORMAN H. YOUNG', JR.

REFERENCES. CITED rihefollowingreferences are of record in the jleyofthis-patent:

'UNl-TEQSTATES. PATENTS.

Number Namev Date` 1,86%;3-2'11 Bagno June. T, 1932 2.,1f4-;6,8,7.f6Zworykin Feb. 141,' `i939 2292134105; Barri-sh Apr. 281, 19.422,347,308@ Cooney. Apr. 18, 19.44 2,363,592 Gollins Novf. 28, 194421,416,329 liabin Feb. 25, 1947- 2,42$i,6213j Deloraine et al. Oct. 28,1947:

FQRElCiN PATENTS..

QQJADUITY. Da? 33 15-y Qreatlritain July2f, 193.9 Salll Great. Britainff- Mar- 6.1933

